Impossible Dovetail Puzzle Box

Riddles are fun, and what are puzzle boxes if not riddles in physical form? This particular box—the “Impossible Dovetail Box”—makes its confusing first impression with a series of dovetail joints that look lovely but don’t make any sense. If the top and bottom halves truly have an identical form on all four sides, there’d be no way for the two pieces to slide into place. So what is really going on here?

As YouTuber Mr. Puzzle demonstrates the box, we can see that it is in fact made of just two separate parts, which eliminates any possibility that there might be some tricky cutting or gluing going on. The box is in fact what it appears to be on the outside, but the inside is where the secrets are. Take a look at the start of the video and see if you can puzzle it out:

This box is actually a few different puzzles at once, and even figuring out one of them can be a challenge, so here are a few hints:

45 degree angles play a very important part in how this works.

Faces that are perpendicular on the outside aren’t necessarily perpendicular on the inside.

Everything slides together with no alteration; these really are two solid pieces of wood.

OK here’s the solution, which you can see by finishing the video above or looking at this image:

Each dovetail extends back at a 45-degree angle from its face, not a 90 degree angle. That means that the dovetails on either side of a corner form a sort of trapezoid and are connected by a slanted track. These two tracks run parallel which means the top can be slid off the bottom at a 45-degree angle.

The box also includes a small ball that can bounce between two magnets. When it is attached to the bottom one, its top half sits between the two blocks, keeping them from sliding apart. But if you slap the box to move the ball to the top magnet, there’s enough clearance for the two halves to slide apart.

All in all it’s a simple but extremely clever design, and one that you could probably replicate at home with a little bit of effort and the right tools. It might not be the most secure place to stash your deepest darkest secrets, but it is certainly a nice puzzle to keep on your desk.